Random blinking pixels

recently a friend of mine called me to help him about a weird problem on his computer. He runs Windows 10 with one monitor and his living room tv attached as second monitor.

Randomly some pixels, or even a lot of pixels, start to light up in a blue-ish green-ish color and blink. Then the screen blacks out a moment and comes back, and the blinking pixels are gone. This happens on both screens but not at the same time.

The first thing that came to mind was a GPU problem so I brought him and old VGA I had around and switched them. To my surprise, the problem persisted.

So I’ve ruled out the GPU and I also ruled out a monitor/cable problem since it happens on both of them.

I’m stumped as I have no clue what this could be.

Any hint or suggestion will be extremely appreciated.